Artificial finger print liquid, testing method for optical information medium using it, and optical information medium

ABSTRACT

The present invention provides a low-cost artificial fingerprint liquid for quantitatively and with a good reproducibility evaluating an anti-staining property, and a fingerprint adhering property or a fingerprint removing property on the surface of an optical disk such as a reproduction-only optical disk, optical recording disk, magneto-optical recording disk, various displays such as a CRT, and various substances such as glass. An artificial fingerprint liquid comprising a fine-particle-form substance and a dispersion medium capable of dispersing the fine-particle-form substance. The dispersion medium preferably has a surface tension ranging from 20 to 50 mN/m at 25° C., and preferably is selected from at least one of higher fatty acid, derivative of higher fatty acid, terpens, and derivatives of terpens. The fine-particle-form substance is at least one selected from inorganic fine particles and organic fine particles. The present invention provides a testing method for an optical information medium using the artificial fingerprint. The present invention provides an optical information medium which is good in the property of wiping off an organic stain, such as a fingerprint, adhering to a surface of the optical recording medium and which can maintain good recording/reproducing property over a long period.

TECHNICAL FIELD

The present invention relates to an artificial fingerprint liquid and,more specifically, an artificial fingerprint liquid for evaluating ananti-staining property, a fingerprint adhering property or a fingerprintremoving property on the surface of various substances. The presentinvention also relates to a testing method for an optical informationmedium such as a reproduction-only optical disk, optical recording diskor magneto-optical recording disk, using the artificial fingerprintliquid. Furthermore, the present invention relates to an opticalinformation medium.

BACKGROUND ART

When an optical disk such as a reproduction-only optical disk, opticalrecording disk, magneto-optical recording disk, various displays such asa CRT, or various substances such as glass are used, the adhesion ofstains or fingerprints to the surface thereof is caused on the basis ofvarious stain materials. The adhesion of these stains or fingerprints isunpreferable, and the surface of the various substances is usuallysubjected to an appropriate surface treatment in order to improve ananti-staining property thereof, decrease a fingerprint adhering propertyor improve a fingerprint removing property.

For example, about an optical disk, investigations are being made onvarious water repellent or oil repellent treatments to the surface ofthe optical disk. In order to check the effect of improving theanti-staining property by the surface treatments, in many cases, thereis used a manner of adhering a fingerprint actually onto the opticaldisk surface and, then, evaluating the wiping-off property thereof withthe naked eye. However, such an evaluating manner is poor inquantitativeness and reproducibility.

On the assumption that if the water repellency or the oil repellency ofthe optical disk surface is high, stain materials are easily removed,the following is frequently performed: measurement of the contact anglesof various liquids, such as water and aliphatic hydrocarbons, to theabove treated-surface. However, the evaluation based on the contactangle or surface free energy is, in a sense, an indirect evaluatingmanner. Accordingly, it can be properly used as a manner for evaluatingthe anti-staining property in only a highly restricted case where theabove-mentioned assumption that if the water repellency or the oilrepellency is high, excellent anti-staining property is exhibited comesinto effect. This evaluating manner gives only a relative evaluationresult at best. In other words, when this evaluating manner is appliedto an optical disk surface, it is substantially impossible that athreshold value which represents whether or not the disk can be usedwithout causing any practical problem is determined for the contactangle or surface free energy.

In recent years, it has been desired that about optical informationmedia the recording density thereof is made higher in order to store amass of data such as moving image data. Thus, researches anddevelopments are being actively made for making the density of recordingcapacity higher. As one of them, the following suggestion is made: asseen in, for example, a DVD, the recording/reproducing wavelengththereof is made short and the numerical aperture (NA) of the objectivelens is made large, thereby making the condensed spot diameter of thereproducing/reproducing beam small. As compared with a CD, a recordingcapacity (4.7 GB/surface) 6 to 8 times that of the CD is actuallyattained by changing the recording/reproducing wavelength from 780 nm to650 nm and changing the numerical aperture (NA) from 0.45 to 0.60.Recently, as a method for recording high-quality moving images for along time, an attempt has been made to make the recording/reproducingwavelength short up to about 400 nm and making the numerical aperturehigh up to 0.85, so as to attain a recording capacity 4 times or morethat of DVD. However, when the recording density is made high in thisway, the condensed spot diameter of the recording/reproducing beambecomes small. Consequently, the recording medium becomes more sensitiveto dust, dirt, fingerprints or the like adhering to the laser beamincident side surface of the medium than the prior art. In particular,about stains containing an organic material, such as fingerprints, alarge effect is produced when the stains adhere to the laser beamincident side surface. Since the stains are not easily removed, manycountermeasures have been considered so far.

For example, Japanese Laid-open Patent Publication Nos. 10-110118 (1998)and 11-293159 (1999) suggest that when a hard coat agent coated film isformed on a surface of an optical disk substrate made of polycarbonateor the like, a non-crosslinking type fluorine type surfactant isincorporated into the hard coat agent. In order to evaluate theanti-staining property of the hard coat surface of the optical disk,there is performed an operation of adhering an artificial fingerprintliquid wherein a small amount of sodium chloride, urea and lactic acidis dissolved in a mixture solution of water and ethanol onto the surfaceof the hard coat under pressure, using a pseudo fingerprint, and thendetermining the wiping-off property thereof with the naked eye. Thisartificial fingerprint liquid is a liquid described in JIS K2246: 1994“Rust Preventing Oil”. The JIS standard prescribes a performance-testingmethod for rust preventing oils used for temporary rust-prevention ofmetal materials such as steel. Accordingly, the artificial fingerprintliquid is prepared to determine the corrosiveness of metal materials.For this reason, the liquid is not useful at all for purposes other thanthis. Even if the artificial fingerprint liquid made mainly of water andethanol is adhered onto a surface of an optical disk substrate made ofresin such as polycarbonate, in reality the artificial fingerprintliquid is repelled and is not fixed on the substrate surface in almostall cases. It can be considered from this fact that the resin substratesurface exhibits the same wiping-off property against the artificialfingerprint liquid whether the surface is not subjected to any surfacetreatment or is subjected to surface treatment. That is, it is hardlysignificant to use the artificial fingerprint liquid prescribed in JISK2246: 1994 for evaluation of the anti-staining property or thefingerprint removing property of an optical disk surface.

From such an actual situation, it is desired to develop an artificialfingerprint liquid for quantitatively and with a good reproducibilityevaluating the anti-staining property, the fingerprint adhering propertyor the fingerprint removing property on an optical disk surface. It isalso desired to develop a testing method for an optical informationmedium using the artificial fingerprint liquid.

DISCLOSURE OF THE INVENTION

Objects of the Invention

Thus, an object of the present invention is to solve the above-mentionedproblems of the prior art and provide a low-cost artificial fingerprintliquid for quantitatively and with a good reproducibility evaluating ananti-staining property, and a fingerprint adhering property or afingerprint removing property on the surface of an optical disk such asa reproduction-only optical disk, optical recording disk,magneto-optical recording disk, various displays such as a CRT, andvarious substances such as glass.

Another object of the present invention is to provide a testing methodfor an optical information medium, using the artificial fingerprintliquid, which makes it possible that when a fingerprint adheres onto thelaser beam incident side surface of the optical information medium, aneffect which recording/reproducing signals receive can be measuredquantitatively and with a good reproducibility.

Still another object of the present invention is to provide an opticalinformation medium which is good in the property of wiping off anorganic stain, such as a fingerprint, adhering to a surface of theoptical recording medium and which can maintain goodrecording/reproducing property over a long period.

SUMMARY OF THE INVENTION

The present invention comprises the following inventions.

(1) An artificial fingerprint liquid comprising a fine-particle-formsubstance and a dispersion medium capable of dispersing thefine-particle-form substance.

In the present description, the dispersion medium means only a liquidcomponent which remains as a pseudo fingerprint component after thecomponent is transferred onto a surface of an object to be evaluated,and is distinguished from a diluent which may be used if necessary whenthe artificial fingerprint liquid is used, most thereof or the wholethereof being finally distilled off after the diluent is transferred.

(2) The artificial fingerprint liquid according to the (1), wherein thedispersion medium has a surface tension ranging from 20 to 50 mN/m at25° C.

(3) The artificial fingerprint liquid according to the (1) or (2),wherein the dispersion medium is at least one selected from higher fattyacid, derivative of higher fatty acid, terpenes, and derivatives ofterpenes.

(4) The artificial fingerprint liquid according to any of the (1) to(3), wherein the fine-particle-form substance has an average particlesize of 100 μm or less.

(5) The artificial fingerprint liquid according to any of the (1) to(4), wherein the fine-particle-form substance is at least one selectedfrom inorganic fine particles and organic fine particles.

(6) The artificial fingerprint liquid according to the (5), wherein thefine-particle-form substance includes, as the inorganic fine particles,any one of silica fine particles, alumina fine particles, iron oxidefine particles, and mixtures of any two or more selected from the fineparticles.

(7) The artificial fingerprint liquid according to the (5) or (6),wherein the fine-particle-form substance includes, as the organic fineparticles, any one of keratin fine particles, chitin fine particles,chitosan fine particles, acrylic type fine particles, styrene type fineparticles, divinylbenzene type fine particles, polyamide type fineparticles, polyimide type fine particles, polyurethane type fineparticles, melamine type fine particles, and mixtures of any two or moreselected from the fine particles.

(8) The artificial fingerprint liquid according to any of the (1) to(7), wherein the fine-particle-form substance includes Kanto loam(powder 1 for a JIS test).

(9) The artificial fingerprint liquid according to any of the (1) to(8), which comprises the fine-particle-form substance at a ratio (weightratio) of 0.1 to 5.0 in relative to the dispersion medium.

(10) The artificial fingerprint liquid according to any of the (1) to(9), which is diluted by a diluent if necessary when the liquid is used.

(11) The artificial fingerprint liquid according to any of the (1) to(10) for evaluating an anti-staining property, a fingerprint adheringproperty, or a fingerprint removing property of various object surfaces.In the present invention, examples of the various objects include anoptical disk such as a reproduction-only optical disk, optical recordingdisk, magneto-optical recording disk, various display such as a CRT, andvarious substances such as glass.

(12) A testing method for an optical information medium, wherein ananti-staining property and/or a fingerprint adhering property of thesurface of the optical information medium which is on the incident sideof a recording/reproducing beam is/are evaluated by adhering anartificial fingerprint liquid comprising a fine-particle-form substanceand a dispersion medium capable of dispersing the fine-particle-formsubstance onto the medium surface which is on the incident side of therecording/reproducing beam.

(13) The testing method for an optical information medium according tothe (12), wherein the anti-staining property and/or the fingerprintadhering property of the surface which is on the incident side of therecording/reproducing beam is/are evaluated by measuring changes inrecording property and/or reproducing property generated by the adhesionof the artificial fingerprint liquid.

(14) The testing method for an optical information medium according tothe (12) or (13), which is applied to the optical information mediumwherein the smallest diameter of the recording/reproducing beam on thesurface which is on the incident side of the recording/reproducing beamis 500 μm or less.

(15) A testing method for an optical information medium, wherein acleaning property and/or a fingerprint removing property of the surfaceof the medium which is on the incident side of a recording/reproducingbeam is/are evaluated by adhering an artificial fingerprint liquidcomprising a fine-particle-form substance and a dispersion mediumcapable of dispersing the fine-particle-form substance onto the mediumsurface which is on the incident side of the recording/reproducing beam,and subsequently performing an operation for removing the artificialfingerprint liquid.

(16) The testing method for an optical information medium according tothe (15), wherein the cleaning property and/or the fingerprint removingproperty of the surface which is on the incident side of therecording/reproducing beam is/are evaluated by measuring changes inrecording property and/or reproducing property generated by theoperation for removing the artificial fingerprint liquid.

(17) The testing method for an optical information medium according tothe (15), which is applied to the optical information medium wherein thesmallest diameter of the recording/reproducing beam on the surface whichis on the incident side of the recording/reproducing beam is 500 μm orless.

(18) An optical information medium which comprises a light-transmittinglayer and an information recording layer and is used to make arecording/reproducing beam incident into the information recording layerthrough the light-transmitting layer,

wherein when an artificial fingerprint liquid comprising afine-particle-form substance and a dispersion medium capable ofdispersing the fine-particle-form substance is adhered onto the surfaceof the light-transmitting layer and subsequently an operation forremoving the adhered artificial fingerprint liquid is performed, thekinetic friction coefficient of the light-transmitting layer surfaceafter the removing operation does not increase by 0.1 or more from thekinetic friction coefficient before the adhesion of the artificialfingerprint liquid.

(19) The optical information medium according to the (18), wherein whena compound having lubricity is present on the light-transmitting layersurface, the amount of the portion not fixed on the light-transmittinglayer surface among the entire compound is 20 mg/m² or less.

(20) The optical information medium according to the (18) or (19),wherein when a layer including a compound which has lubricity and is notfixed on the light-transmitting layer surface is present on thelight-transmitting layer surface, the thickness of the above layer is 10nm or less.

(21) The optical information medium according to any of the (18) to(20), wherein the kinetic friction coefficient of the light-transmittinglayer surface is 0.4 or less before the adhesion of the artificialfingerprint liquid.

(22) The optical information medium according to any of the (18) to(21), wherein a Si—O bond is present in at least one portion of thelight-transmitting layer surface.

(23) The optical information medium according to any of the (18) to(22), wherein at least one portion of the light-transmitting layersurface includes a fluorine atom.

(24) The optical information medium according to any of the (18) to(23), wherein at least one portion of the light-transmitting layersurface is made of a silane coupling agent which includes a groupexhibiting water repellency or oil repellency and which is representedby the following formula (I):R₁—Si(X)(Y)(Z)  (I)[wherein R₁ is a substituent having water repellency, oil repellency orlubricity, X, Y and Z are each a monovalent group, and at least one ofX, Y and Z is a substituent capable of forming a chemical bond bypolycondensation with a hydroxyl group.]

(25) The optical information medium according to any of the (18) to(24), wherein the light-transmitting layer surface is fluorinated byplasma treatment.

(26) The optical information medium according to any of the (18) to(25), wherein at least one portion of the light-transmitting layer ismade of diamond-like carbon.

(27) The optical information medium according to any of the (18) to(26), which is used in a system wherein the smallest diameter of arecording/reproducing beam on the light-transmitting layer surface is500 μm or less.

(28) An optical information medium which comprises a light-transmittinglayer and an information recording layer and is used to make arecording/reproducing beam incident into the information recording layerthrough the light-transmitting layer, wherein when an artificialfingerprint liquid comprising a fine-particle-form substance and adispersion medium capable of dispersing the fine-particle-form substanceis adhered onto the surface of the light-transmitting layer andsubsequently an operation for removing the adhered artificialfingerprint liquid is performed, the contact angle of water to thelight-transmitting layer surface after the removing operation does notdecrease by 15% or more from the contact angle thereof before theadhesion of the artificial fingerprint liquid.

(29) The optical information medium according to the (28), wherein whena compound having water repellency is present on the light-transmittinglayer surface, the amount of the portion not fixed on thelight-transmitting layer surface among the entire compound is 20 mg/m²or less.

(30) The optical information medium according to the (28) or (29),wherein when a layer including a compound which has water repellency andis not fixed on the light-transmitting layer surface is present on thelight-transmitting layer surface, the thickness of the above layer is 10nm or less.

(31) The optical information medium according to any of the (28) to(30), wherein before the adhesion of the artificial fingerprint liquid,the contact angle of water to the light-transmitting layer surface is75° or more at 20° C.

(32) The optical information medium according to any of the (28) to(31), wherein before the adhesion of the artificial fingerprint liquid,the contact angle of water to the light-transmitting layer surface is90° or more at 20° C.

(33) The optical information medium according to any of the (28) to(32), wherein a Si—O bond is present in at least one portion of thelight-transmitting layer surface.

(34) The optical information medium according to any of the (28) to(33), wherein at least one portion of the light-transmitting layersurface includes a fluorine atom.

(35) The optical information medium according to any of the (28) to(34), wherein at least one portion of the light-transmitting layersurface is made of a silane coupling agent which includes a groupexhibiting water repellency or oil repellency and which is representedby the following formula (I):R₁—Si(X)(Y)(Z)  (I)[wherein R₁ is a substituent having water repellency, oil repellency orlubricity, X, Y and Z are each a monovalent group, and at least one ofX, Y and Z is a substituent capable of forming a chemical bond bypolycondensation with a hydroxyl group.]

(36) The optical information medium according to any of the (28) to(35), wherein the light-transmitting layer surface is fluorinated byplasma treatment.

(37) The optical information medium according to any of the (28) to(36), wherein at least one portion of the light-transmitting layer ismade of diamond-like carbon.

(38) The optical information medium according to any of the (28) to(37), which is used in a system wherein the smallest diameter of arecording/reproducing beam on the light-transmitting layer surface is500 μm or less.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view illustrating a structural exampleof an optical information medium.

FIG. 2 is a schematic sectional view illustrating another structuralexample of the optical information medium.

FIG. 3 is a schematic sectional view of an optical recording disk sampleused in Examples.

FIG. 4 is a graph showing a relationship between the number of wipes ofa pseudo fingerprint adhering to the surface of the optical recordingdisk and the jitter of the optical recording disk in Example 3.

MODES FOR CARRYING OUT THE INVENTION

First, an artificial fingerprint liquid of the present invention will bedescribed.

The artificial fingerprint liquid of the present invention comprises afine-particle-form substance and a dispersion medium capable ofdispersing the fine-particle-form substance. The dispersion mediumpreferably has a surface tension ranging from 20 to 50 mN/m at 25° C. Bysuch a constituent, the artificial fingerprint liquid is made up to anartificial fingerprint liquid having a character as close as possible toan actual fingerprint. Thus, the artificial fingerprint liquid can besuitably used for evaluating an anti-staining property, a fingerprintadhering property, or a fingerprint removing property on varioussubstance surfaces.

In the case that an artificial fingerprint liquid of a homogeneouscomponent system made only of a liquid is used at this time, the liquiddoes not approximate to the removing property of any actual fingerprint.For example, in the case that triolein, which is one ofsebum-constituting components, is used as the homogeneous system, thesurface tension of triolein is 34 mN/m at 25° C. Therefore, the surfaceof polytetrafluoroethylene (PTFE), which has a critical surface tensionof about 18 mN/m, repels triolein completely without getting wet.However, actual fingerprints never fail to be fixed even on the PTFEsurface. This is mainly because any fingerprint is not made only of aliquid substance but is made of an inhomogeneous system containing aninsoluble material and a viscous material. Accordingly, by making aninhomogeneous system wherein an appropriate insoluble component is addedto a dispersion medium made of a liquid component contained in an actualfingerprint and/or a liquid similar thereto, the artificial fingerprintliquid of the present invention having a character as close as possibleto an actual fingerprint can be obtained.

Herein, critical surface tension will be described. The water repellencyand the oil repellency of a material can be represented into one way bycritical surface tension (γ_(c)/mNm⁻¹), which is a criterion of thesurface free energy of the material. The critical surface tension can beobtained from an actually-measured value of the contact angle thereof.Specifically, the contact angle (θ/rad) to a smooth surface made of aspecified material is measured about several saturated hydrocarbonliquids each having a known surface tension (surface tension: γ₁/mNm⁻¹).A value extrapolated to cos θ=1 in plots of cos θ and γ₁ is the criticalsurface tension γ_(c) of the specified material. In order that somematerial can repel a liquid, it is necessary that the critical surfacetension γ_(c) of the material is less than the surface tension γ₁ of theliquid. For example, γ_(c) of a material having a surface composition ofa methylene chain (—CH₂—)_(n) is 31 mNm⁻¹. Accordingly, the materialrepels water, which has a surface tension γ₁ of 73 mNm⁻¹ at atemperature of 20° C., but completely gets wet to n-hexadecane, whichhas a surface tension γ₁ of 28 mNm⁻¹. The contact angle thereof turns to0 degree.

The artificial fingerprint liquid of the present invention comprises afine-particle-form substance in the dispersion medium. The majority ofsolid components contained in any actual fingerprint is a protein calledkeratin. In the simplest way, therefore, fine powders of keratin areadded to and mixed with the dispersion medium having the above physicalproperty values, so that the artificial fingerprint liquid of thepresent invention can be prepared. Indeed, a mixture wherein keratinfine powders are mixed with a dispersion medium, such as water, oleicacid, squalane or triolein, at an appropriate ratio can be effectivelyused as the artificial fingerprint liquid of the present invention.However, generally available keratin is remarkably expensive. Thus, alarge amount thereof cannot be easily obtained. Furthermore,commercially available keratin has a different particle sizedistribution from that of keratin contained in actual fingerprints. Itis therefore necessary to adjust the particle size distribution thereofin advance if necessary. Accordingly, it cannot be necessarily said thatthe method of using commercially available keratin is a preferablemethod from the viewpoint of simplicity, measurement precision and itsreproducibility.

In order to solve the problems of keratin, the present inventorsresearched a fine-particle-form substance which can be used instead ofkeratin. As a result, it has been found that fine particles having agood wettability to the dispersion medium having the above physicalproperty values and having particle sizes close to that of keratincontained in actual fingerprint components are preferable as thefine-particle-form substance.

The artificial fingerprint liquid of the present invention includes atleast one selected from inorganic fine particles and organic fineparticles as the fine-particle-form substance. The inorganic fineparticles, which are not particularly limited, may be, for example,silica fine particles, alumina fine particles, iron oxide fineparticles, and mixtures of any two or more selected from the fineparticles. The organic fine particles, which are not particularlylimited, may be, for example, keratin fine particles, chitin fineparticles, chitosan fine particles, acrylic type fine particles, styrenetype fine particles, divinylbenzene type fine particles, polyamide typefine particles, polyimide type fine particles, polyurethane type fineparticles, melamine type fine particles, and mixtures of any two or moreselected from the fine particles.

All of the inorganic fine particles exhibit, as the constitutingcomponent of the artificial fingerprint liquid, the same effect askeratin fine particles, and are further more inexpensive than thekeratin fine particles. Therefore, in order to decrease costs and makethe performance stable, the content of the inorganic fine particles ispreferably 50% by weight or more, more preferably 80% by weight or more,and considerably preferably 100% by weight of the whole of thefine-particle-form substance. It is advisable that organic fineparticles such as keratin fine particles may be used together ifnecessary. Among the organic fine particles, acrylic type fineparticles, styrene type fine particles, divinylbenzene type fineparticles, polyamide type fine particles, polyimide type fine particles,polyurethane type fine particles, melamine type fine particles and thelike are preferable since they are relatively inexpensive.

The fine-particle-form substance preferably has an average particle size(that is, median diameter) of 100 μm or less, and more preferably has anaverage particle size of 50 μm or less. Examples of thefine-particle-form substance which includes an inorganic component andhas an average particle size of 100 μm or less include JIS Z8901 testingpowders 1 and 2, ISO testing powder 12103-1, and the Association ofPowder Process Industry and Engineering Japan (APPIE) standard powder.All the testing powders are preferable since they have uniform particlesizes and are available at a relatively low cost. Among examples of theJIS Z8901 testing powder 1, Kanto loam is preferable. It is allowable touse, besides the respective testing powders per se, at least one ofinorganic fine particles contained in the respective testing powders,for example, at least one selected from various oxide fine particlessuch as SiO₂, Fe₂O₃ and Al₂O₃. The average particle size of thefine-particle-form substance is preferably 0.05 μm or more, morepreferably 0.5 μm or more. Accordingly, the average particle size of thefine-particle-form substance is preferably 0.05 μm or more and 100 μm orless, more preferably 0.5 μm or more and 50 μm or less. If thefine-particle-form substance is too large or too small, the substratecannot exhibit easily a sufficient function as an alternate material ofkeratin contained in actual fingerprints.

The fine-particle-form substance preferably has a critical surfacetension at 25° C. larger than that of the used dispersion medium at 25°C., and the critical surface tension is preferably 40 mN/m or more, morepreferably 50 mN/m or more. All of the above particles exemplified asthe inorganic fine particles have such a desired nature about thecritical surface tension.

In the present invention, as the dispersion medium, there is preferablyused a liquid having a surface tension ranging from 20 to 50 mN/m at 25°C. and a saturated vapor pressure of 760 mmHg (101325 Pa) or less at200° C. The liquid which constitutes sweat or sebum of human beings or aliquid having a character close to it usually has such physical propertyvalues. Accordingly, it is advisable to use a liquid having the physicalproperty values as the dispersion medium of the artificial fingerprintliquid in the present invention. If the surface tension is less than 20mN/m at 25° C., the wettability to the surface of an object to beevaluated becomes too high, so that the artificial fingerprint liquidadheres far more easily onto the object surface and is more difficultlyremoved than actual fingerprints. On the other hand, if the surfacetension exceeds 50 mN/m at 25° C., the wettability to the object surfaceto be evaluated lowers, so that the artificial fingerprint liquidadheres far more difficultly onto the object surface and is more easilyremoved than actual fingerprints.

If the saturated vapor pressure exceeds 760 mmHg (101325 Pa) at 200° C.,the dispersion medium volatilizes gradually after the adhesion of thefingerprint onto the object surface to be evaluated, so that the stateof the adhering artificial fingerprint may change in a short time. Whatdegree of easiness of the volatilization of the dispersion medium isafter the adhesion of the fingerprint onto the object surface to beevaluated is also affected by the temperature of the object surface tobe evaluated, the temperature of the use environment of the artificialfingerprint liquid, or the like.

In the present invention, it is desirable that the viscosity of theliquid used as the dispersion medium is preferably 500 cP or less, morepreferably from 0.5 to 300 cP, and still preferably from 5 to 250 cP at25° C. By having such a viscosity, the dispersion medium causes thefine-particle-form substance to be satisfactorily dispersed and beeasily fixed to the object surface even after the adhesion of thefingerprint onto the object surface to be evaluated.

The dispersion medium is not particularly limited, and examples thereofinclude higher fatty acid, derivatives of higher fatty acid, terpenes,and derivatives of terpenes. Examples of the higher fatty acid includevarious acids such as oleic acid, linoleic acid, linolenic acid. Thederivatives of higher fatty acid may be ester derivatives, and examplesthereof include diglyceride derivatives and triglyceride derivatives(for example, triolein). The terpenes may be various terpenes, andexamples thereof include squalane, limonene, α-pinene, β-pinene,camphene, linalool, terpineol, and cadinene. It is advisable to selectat least one from these and use the selected one alone or the selectedtwo or more in a mixture form. It is also preferable to mix one or morethereof with water and use the mixture.

In the present invention, an appropriate mixing ratio between thefine-particle-form substance and the dispersion medium depends on themethod of adhering the artificial fingerprint liquid onto the objectsurface to evaluated, which method will be described later, and others.Therefore, the mixing ratio cannot be specified without reservation. Ingeneral, however, 0.1 to 5.0 weights of the fine-particle-form substanceare preferably added per weight of the dispersion medium, and 0.1 to 3.0weights of the fine-particle-form substance are more preferably added.If the mixing ratio of the fine-particle-form substance to thedispersion medium is too low or too high, it becomes difficult that theresultant functions effectively as an artificial fingerprint liquid. Ifthe fine-particle-form substance is at a ratio less than 0.1, the effectof the addition of the fine-particle-form substance is not obtained, sothat the artificial fingerprint liquid is not easily fixed on the objectsurface to be evaluated or the liquid tends to be easily removed even ifthe liquid is fixed. On the other hand, if the fine-particle-formsubstance is added at a ratio over 5.0, liquid crosslinking effect,based on the dispersion medium, on the object surface to evaluateddeteriorates, so that the artificial fingerprint liquid tends not to beeasily fixed.

The dispersion medium means only liquid components remaining as pseudofingerprint components after they are transferred to the object surfaceto be evaluated, and does not include a diluent which will be describedlater.

In the present invention, it is preferable to add a wax, that is, anester of higher fatty acid and monovalent alcohol to these dispersionmedium components, which are liquid at ambient temperature, so as tomake the viscosity of the dispersion medium components high. As the wax,for example, the following may be used: a natural wax such as candelillawax, carnauba wax, urucury wax, rice wax, sugar wax, wood wax, beeswax,spermaceti, Chinese insect wax, shellac wax, or montan wax; or asynthetic wax such as cholesteryl stearate, myristyl myristate, or cetylpalmitate. The addition percentage of each of the waxes may beappropriately determined in accordance with the property of the objectto be evaluated, for example, the property of the recording/reproducingoptical system of an optical disk, the purpose of the evaluation, andothers.

A general thickener may be added to the artificial fingerprint liquid,examples thereof including carrageenan, gum arabic, xanthan gum,galactomannan, and pectin. Furthermore, in order to improve thedispersibility of the fine-particle-form substance, various surfactantsmay be added, examples thereof including quaternary ammonium salts,alkylbenzenesulfonates, and polyoxyethylene polyoxypropylene glycol.

In the present invention, the artificial fingerprint liquid may bediluted with a diluent such as isopropyl alcohol, methyl ethyl ketone ormethoxypropanol if necessary in order to improve the transferringproperty of the artificial fingerprint. Most of these diluents or thewhole thereof are finally distilled off after they are transferred tothe object surface to be evaluated. The diluent usually has a saturatedvapor pressure exceeding 760 mmHg (101325 Pa) at 200° C. It is allowableto add ethanol, liquid paraffin or the like appropriately to theartificial fingerprint liquid.

In a way as described above, the artificial fingerprint liquid of thepresent invention is composed.

Next, a testing method for an object surface, using the artificialfingerprint liquid of the present invention will be described.

When the artificial fingerprint liquid of the present invention isadhered to a surface of an object to be evaluated, it is preferable touse a pseudo fingerprint transferring stamp made of elastomer.Specifically, it is preferable to produce a pseudo fingerprinttransferring stamp made of silicone rubber, butadiene rubber, urethanerubber or the like and use this. The pseudo fingerprint transferringstamp may be made into such a shape that a fingerprint pattern isprecisely copied from a mold which is actually obtained from man'sfingers. In a simpler way, it is preferable to use a rubber plug forprinting an artificial fingerprint liquid prescribed in JIS K2246-1994.That is, it is possible to use, as the pseudo fingerprint transferringstamp, a material the surface of which is roughened by polishing a smallcircular surface (diameter: about 26 mm) of a No. 10 rubber plug with anAA240 polishing agent prescribed in JIS R6251 or JIS R6252 or apolishing agent having performance similar thereto. However, withoutlimitation to the above-mentioned material, a material capable of givingsubstantially the same pseudo fingerprint transferring property asdescribed above can be preferably used. In order to obtain a size closeto that of an actual fingerprint, an object having a smaller diameterthan the above-mentioned rubber plug is preferably used. Specifically, arubber plug having a diameter of 8 to 25 mm is preferably used, and arubber plug having a diameter of 8 to 20 mm is more preferably used.

The method of using such a pseudo fingerprint transferring stamp totransfer the artificial fingerprint liquid of the present invention, asa pseudo fingerprint, onto an object surface to be evaluated, such as anoptical disk, can be appropriately determined in accordance with thepurpose of the evaluation. For example, an original plate for pseudofingerprint pattern transfer is previously produced, and the rubber plugis used to transfer a pseudo fingerprint from this original plate ontothe object surface to be evaluated. Specifically, the artificialfingerprint liquid is uniformly applied onto a rigid substrate made ofglass or resin. As the coating method at this time, an appropriatemethod may be used from various coating methods such as spin coating anddip coating methods. When the artificial fingerprint liquid is appliedonto the substrate, the liquid may be diluted with an appropriateorganic solvent such as isopropyl alcohol or methyl ethyl ketone inorder to obtain a good application property. It is advisable to distilloff these diluents by air drying or heat drying after the application.In this way, the substrate onto which the artificial fingerprint liquidis uniformly applied is produced and this is used as an original platefor pseudo fingerprint pattern transfer.

The pseudo fingerprint transferring stamp is pressed, under apredetermined load, against the surface of this original plate ontowhich the artificial fingerprint liquid is applied, so as to transferthe artificial fingerprint liquid component onto the transferring stamp.Thereafter, the transferring stamp onto which the artificial fingerprintliquid component is transferred is pressed under a predetermined loadagainst the object surface to be evaluated, so as to transfer the pseudofingerprint pattern onto the object surface to be evaluated.

The use of the above-described method makes it possible to evaluate,with a good reproducibility, the pseudo fingerprint adhering property inthe transferring and further to evaluate, with a good reproducibility,the property for removing the pseudo fingerprint adhered by thetransferring. In this way, the anti-staining property of various objectsurfaces can be quantitatively evaluated with a high reproducibilityaccording to the present invention.

Next, an optical information medium of the present invention, which hasan improved fingerprint removing property, will be described.

In order to realize an optical information medium having a goodfingerprint removing property when a fingerprint removing propertytesting method based on the above-mentioned artificial fingerprintliquid component is used, the present inventors made variousinvestigations. As a result, it has been made clear that an opticalinformation medium having characters detailed below is desirable.

A structural example of the optical information medium of the presentinvention is illustrated in FIG. 1. This optical information medium is arecording medium and has, on a relatively high rigid supportingsubstrate 20, and a recording layer 4 as an information recording layer.The optical information medium has, on this recording layer 4, alight-transmitting layer 2 which is relatively thin and preferably has athickness of 30 to 300 μm.

Influence, based on adhesion of a fingerprint, on recording/reproducingproperty depends on the diameter of a laser beam (the smallest diameterin the case that the beam section is elliptic) on the medium surfacewhich is on the incident side of the laser beam. When this diameter issmall, large influences as follows are produced: continuous errors,which cannot be corrected, are made. The present inventors' research hasdemonstrated that in the case that the diameter of the laser beamincident side surface of the medium is 500 μm or less, in particular,300 μm or less, bad influence on the recording/reproducing propertybecomes remarkable when a fingerprint adheres to the medium which isbeing handled. The diameter of the laser beam, on the laser beamincident side surface of the medium, is represented as follows:2t·tan{sin⁻¹(NA/n)}wherein the thickness of the light-transmitting layer 2 in FIG. 1 isrepresented by t, the refractive index of the light-transmitting layer 2is represented by n, and the numerical aperture of the objective lens ofthe recording/reproducing optical system is represented by NA.

The present invention can be applied regardless of the kind of therecording layer. That is, the present invention can be applied to arecording medium whether the medium is, for example, a phase-change typerecording medium, a bit-forming type recording medium or amagneto-optical recording medium. Usually, a dielectric layer or areflective layer for protecting the recording layer or attaining anoptical effect is laid on at least one side of the recording layer.However, the above laid layer is not shown in FIG. 1. The presentinvention can be applied to a reproduction-only type, as well as arecordable type as illustrated. In this case, a pit row integrated withthe supporting substrate 20 is formed, and a reflective layer (metallayer or dielectric multilayered film) covering the pit row constitutesan information recording layer.

The present invention can also be applied to an optical informationmedium of a structural example illustrated in FIG. 2. The mediumillustrated in FIG. 2 has, on a light-transmitting layer 2, a recordinglayer 4 and a protective layer 6 in this order. In this structuralexample, the light-transmitting layer 2 having a relatively highrigidity is used, and the light-transmitting layer 2 also plays a roleof a supporting substrate. The two media each having the structureillustrated in FIG. 1 or FIG. 2 are adhered to each other so as to causethe light-transmitting layers 2 to face outwards, so that a two-sidedrecording type medium can be produced.

In both of the FIGS. 1 and 2, the outer surface of thelight-transmitting layer 2 constitutes the laser beam incident sidesurface of the medium. The recording or reproducing laser beam is madeincident into the recording layer 4 through the light-transmitting layer2.

In order to attain desired performances, the light-transmitting layer 2may be made into an embodiment made of two or more different layers. Asone example thereof, a structure wherein the light-transmitting layer 2is composed of two layers of an inner layer 2 i and a surface layer 2 sis illustrated in FIGS. 1 and 2.

In the medium of the present invention, the contact angle of water tothe surface of the light-transmitting layer 2 which is on the incidentside of the laser beam is preferably 75° or more, more preferably 90° ormore at 20° C. The upper limit of the contact angle is not particularlyspecified, and is generally about 150°. Even if the contact angle israised to 100° or more, the wiping-off property of fingerprints is notremarkably improved.

Incidentally, examples of means for attaining a contact angle of 90° ormore, more specifically about 100° include a method of incorporating anon-crosslinking, fluorine type surfactant into a hard coat agent asdescribed in Japanese Laid-open Patent Publication Nos. 10-110118 (1998)and 11-293159(1999); and a method of applying a fluorine-containingpolymer, a typical example of which is perfluoropolyether, onto thesurface of the light-transmitting layer as disclosed in JapaneseLaid-open Patent Publication No. 2000-082236. There is also known amethod of using, for example, a silicone-type polymer or the like, aswell as the fluorine-containing compound.

However, in the case of the method of incorporating a fluorine type or asilicone type surfactant excellent in water repellency and oilrepellency into a hard coat, water repellency and oil repellency areexhibited by the surfactant exuding onto the surface of the hard coat;therefore, the exuding surfactant is removed from the hard coat surfacewhen a fingerprint is wiped off. Consequently, the water repellency ofthe hard coat surface is largely deteriorated by the wipe of thefingerprint. Since the exuding surfactant is not fixed onto the hardcoat surface, the surfactant has fluidity. Accordingly, the fingerprintcomponent adhering onto the hard coat surface is blended with thesurfactant. The blend of the surfactant with the fingerprint componentis further promoted by the wiping work of the fingerprint. Conversely,therefore, it becomes difficult to remove the fingerprint by the wipingwork. A similar problem is caused in the method of applying the fluorinetype polymer or the silicone type polymer onto the surface of thelight-transmitting layer.

In Japanese Laid-open Patent Publication No. 11-293159 (1999), as thesurfactant incorporated into the hard coat, the following two aretogether used: a non-crosslinking fluorine type surfactant which iseasily wiped off and a crosslinking fluorine-type surfactant good inwiping-off resistance. However, in the invention described in the samepublication, the crosslinking fluorine type surfactant compensates forthe anti-staining property after the non-crosslinking fluorine typesurfactant is wiped off, as described in paragraphs [0021] to [0023] ofthe publication. That is, the invention described in the samepublication is not any invention for solving the promotion of the blendof the surfactant with the fingerprint component by the wiping-off workof fingerprints.

Such a fatal problem has not been pointed out so far. This is becausethere has not existed any method for testing fingerprint removingproperty quantitatively wherein the adhesion of an actual fingerprint issatisfactorily imitated.

Accordingly, about the optical information medium of the presentinvention, especial attention should be paid so as not to cause blend ofa fluid component present on the surface of the light-transmitting layerwith an adhering fingerprint component. It can easily be checked whetheror not the fluid component miscible with the fingerprint component ispresent on the light-transmitting layer surface by the following method.

In the case that the fluid component contains a compound havinglubricity, the presence of the fluid component can be checked byperforming an operation for wiping off the light-transmitting layersurface with a cloth and then examining a change in the kinetic frictioncoefficient before and after the wiping-off operation. Specifically, acloth (for example, Bemcot Lint Free CT-8, manufactured by AsahiChemical Industry Co., Ltd.) is impregnated with the artificialfingerprint liquid component, and then the light-transmitting layersurface is scrubbed 6 to 400 times, preferably 10 to 200 times at a loadof 1.0 to 10 N/cm². Thereafter, a volatile organic solvent such asmethanol, ethanol, methyl ethyl ketone or acetone is used to perform anoperation for removing the artificial fingerprint liquid componentremaining on the light-transmitting layer surface. Moreover, the kineticfriction coefficient of the surface is measured. Instead of removing theartificial fingerprint liquid component with the volatile organicsolvent, the optical information medium may be heated to perform anoperation for distilling off the artificial fingerprint liquidcomponent.

When the kinetic friction coefficient after the artificial fingerprintliquid component is wiped off with the cloth increases by 0.1 or morefrom the kinetic friction coefficient at the initial stage (before thewiping), a significant amount of the fluid component may be regarded asbeing present on the light-transmitting layer surface. Conversely, ifthe increase amount of the kinetic friction coefficient is less than0.1, bad influence is hardly produced on the fingerprint removingproperty even if a very small amount of the fluid component is present.The kinetic friction coefficient is preferably measured by a methodwhich will be described later.

In the case that the fluid component contains a compound having waterrepellency, the presence of the fluid component can be checked byexamining a change in the contact angel of water before and after thewiping-off operation. In this case, a significant amount of the fluidcomponent may be regarded as being present on the light-transmittinglayer surface if the contact angle after the wiping-off operationdecreases by 15% or more of the contact angle at the initial stage(before the wiping). Conversely, if the decrease amount of the contactangle is less than 15%, bad influence is hardly produced on thefingerprint removing property even if a trace amount of the fluidcomponent is present.

In order that in the measurement of the change in the kinetic frictioncoefficient the increase amount of the kinetic friction coefficient willbe less than 0.1 or in the measurement in the change in the contactangle the decrease amount of the contact angle will be less than 15%,the amount of the fluid component, that is, the amount of the compoundnot fixed on the light-transmitting layer surface by chemical bonds orthe like (the existence amount thereof per unit area of thelight-transmitting layer) is preferably set into 20 mg/m² or less, morepreferably 10 mg/m² or less, and still more preferably 5 mg/m² or less.The thickness of the layer made of the fluid component on thelight-transmitting layer surface is preferably set into 10 nm or less,more preferably 5 nm or less, and still more preferably 2 nm or less.

Furthermore, in the optical information medium of the present invention,it is desirable to make the abrasion or wear resistance and the scratchresistance of the surface high in order not to generate scratches andothers in the light-transmitting layer surface even if the operation forwiping off an adhering fingerprint is repeated. Specifically, the pencilhardness measured by the method according to JIS K5600-5-4:1999 (ISO/DIS15184:1996) is preferably B or more, more preferably HB or more.

In a wear testing method based on abrasive wheels according to ISO9352:1995, ΔHaze (%) measured under the following conditions ispreferably 15% or less, more preferably 7% or less. That is, thecloudiness value is measured with a haze meter after a CS-10F is used asthe abrasive wheels and 100-rotation wear is carried out under a load of4.9 N. At this time, as a testing sample, a light-transmitting layer onwhich a reflective film or an information recording layer such as aphase-change film is not formed is used. In the case of the low rigidlight-transmitting layer 2 made of a resin layer or a resin sheet asillustrated in FIG. 1, a sample wherein the light-transmitting layer 2is formed, without forming any information recording layer, directlyonto the supporting substrate 20 is used as the testing sample. In thecase that the supporting substrate 20 is not transparent in an actualmedium, the following is used instead of the actual supporting substrate20: a supporting substrate made of a transparent resin such aspolycarbonate, methyl methacrylate, or amorphous polyolefin.

An optical information medium excellent in the property for removing anadhering fingerprint can be realized by using a light-transmitting layeras described above, wherein: the contact angle of water is 75° or more;a decrease in the contact angle of water and an increase in the kineticfriction coefficient are kept less than 15% of the initial value andless than 0.1 thereof, respectively, after the artificial fingerprintliquid component is adhered and then removed; the pencil hardness is Bor more; and the cloudiness value after the wear test is 15% or less.

However, even about such an optical information medium excellent infingerprint removing property, there is a case in which when a useractually performs an operation for wiping off stains, the user feelsthat the wiping-off is not easy. Even about an optical informationmedium which is not really excellent in fingerprint removing property,there is a case in which the user feels that stains are easily wipedoff. It has been found that such dissociation between the actualfingerprint removing property and user's feeling that the wiping-off iseasy depends on the magnitude of the kinetic friction coefficient of thelight-transmitting layer surface in most cases. That is, when thekinetic friction coefficient of the light-transmitting layer surface islow, it is felt that the wiping-off is easy even if the actualfingerprint removing property is poor. Conversely, when the kineticfriction coefficient of the surface is high, it is felt that thewiping-off is difficult even if the actual fingerprint removing propertyis excellent. This is because, for example, it is felt that the cloth iscaught at the time of the wiping-off.

In principle, actual fingerprint wiping-off property is regarded as moreimportant than sensuous fingerprint wiping-off property. It is howeverdesired that no dissociation is present between such sensuousfingerprint wiping-off property which human beings feel and actualfingerprint wiping-off property, which is quantitatively measured, sinceusers actually perform wiping works by hand.

The inventors repeated investigation on correlation between themagnitude of the kinetic friction coefficient and the above-mentionedsensuous fingerprint removing property. As a result, it has been provedthat when the kinetic friction coefficient of the light-transmittinglayer surface is 0.4 or less, preferably 0.3 or less, the fingerprintwiping-off property can be considered to be good regardless of otherproperties such as surface hardness, water repellency and oilrepellency.

The kinetic friction coefficient is preferably measured according to thetesting method prescribed in ISO 8295:1995. However, some other methodmay be used if the method does not give a remarkably different measuredvalue. However, even if any testing method is used, it is preferable touse, as a slider, a rectangular or circular piece the contact area ofwhich to the light-transmitting layer surface is 4.0 cm² or less. Thecontact area of the slider to the light-transmitting layer surface maybe substantially zero. That is, the slider may undergo point contact.When the slider is caused to undergo point contact, the curvature radiusof the above slider is preferably set into 0.1 to 10 mm. The loadapplied to a test piece by the slider is controlled into a constantvalue within the range of 1.0×10⁻³ to 9.8×10⁻¹ N regardless of thecontact area. Usually, in the above-mentioned testing method describedin ISO 8295:1995, two test pieces made of the same material are madeinto a pair and the test is made in the state that these test pieces arebrought into contact with each other. However, in the case that it isevident that substantially the same result as in this case can beobtained, the raw material of the test piece on which the slider is putmay be changed to raw material different from the material the kineticfriction coefficient of which is desired to be measured. For example, asthe test piece on which the slider is put, a flat and smooth glass plateor plastic material can be used. Specific examples of the plasticmaterial include various resins such as nylon, polypropylene, polyester,polyimide, polyarylate, and polyacetal. The slider per se may alsofunction as one of the test pieces without preparing the slider and thetest piece on which the slider is put separately.

The optical information medium satisfying all of the requirementsdetailed above can be realized, for example, by the following method.That is, the inner layer 2 i in the light-transmitting layer 2 is madeup to a layer made of a thermoplastic resin or a radiation curableresin; the surface layer 2 s formed to contact this is made of atransparent material excellent in abrasion resistance and scratchresistance as compared with the inner layer 2 i; and further the surfaceof the surface layer 2 s is subjected to treatment for giving waterrepellency, oil repellency and lubricity. The radial ray in thedescription is a concept including both of an electromagnetic wave, suchas an ultraviolet ray, and a particle ray, such as an electron ray.

The whole of the light-transmitting layer 2 may be made of a transparentmaterial excellent in abrasion resistance and scratch resistance.However, the light-transmitting layer 2 is preferably composed of theinner layer 2 i and the surface layer 2 s, which are separated form eachother, as described above since a large warpage is easily generated inthe light-transmitting layer made of a highly hard resin.

The inner layer 2 i is preferably a substrate or sheet made of athermoplastic resin such as polycarbonate, polymethyl methacrylate oramorphous polyolefin, or a coating made of a radiation curable resin, atypical example of which is acrylic ultraviolet curable resin.

As the material of the surface layer 2 s, a radiation curable resin maybe used, examples of which include acrylic ultraviolet curable resin andepoxy ultraviolet curable resin. It is however necessary to select aresin material having a tensile elasticity or Young's modulus after theresin is set higher than that of the resin used as the material of theinner layer 2 i. In order to make the abrasion resistance and thescratch resistance of the light-transmitting layer surface sufficient,it is preferable to add inorganic fine particles made of colloidalsilica or the like into the resin material in advance and make a statethat the inorganic fine particles are dispersed in the coating afterbeing hardened. Specifically, inorganic fine particles made of silica,alumina, titanina, zirconia, titanium nitride, aluminum nitride, siliconcarbide, calcium carbide or the like are added to a radiation curableresin matrix in such a manner that the percentage thereof in theresultant film after being hardened will be set into 5 to 80%, morepreferably 10 to 60% by weight. If necessary, the resultant mixture isthen diluted with a non-reactive organic solvent. Furthermore, themixture is applied onto the surface of the inner layer 2 i and hardened.The average particle size of the added inorganic fine particles ispreferably 100 nm or less, more preferably 50 nm or less. An example ofa commercially available product of the radiation curable resin in whichinorganic fine particles are dispersed is a Desolight Z7503(manufactured by JSR Co., Ltd.).

As the material of the surface layer 2 s, a thermoset organiccomposition can be preferably used. After the thermosetting, a part oforganic groups thereof may remain, or the organic composition may turnto a substantially complete inorganic compound. As such a composition, acomposition having a Si—O bond is preferable. Specifically, thefollowing may be used: a hardened coating formed from a solutioncontaining an organic silicon compound such as tetraalkoxysilane bysol-gel process; a thin film made mainly of SiO₂ formed from apolysilazane solution through hydrolysis reaction; or the like. Thematerial which makes the hardened coating containing SiO₂ by sol-gelprocess is a TS-56 (manufactured by Tokuyama Corp.) as a commerciallyavailable product, or the like. The material which makes the hardenedcoating made mainly of SiO₂ from polysilazane is an N-L110 (manufacturedby Tonen general Sekiyu K.K.) as a commercially available product.

An inorganic and/or organic thin film formed by a vacuum film-formingmethod, such as sputtering or ion plating, can also be preferablyapplied.

The thickness of the surface layer 2 s made of the radiation curableresin is preferably set into from 0.2 to 10 μm, more preferably from 0.5to 5.0 μm. On the other hand, in the case that the inorganic thin filmformed by a thermosetting process, such as sol-gel process, or a vacuumfilm-forming method, such as sputtering, is used as the material of thesurface layer 2 s, the film thickness thereof preferably ranges from 10to 1000 nm, more preferably from 30 to 500 nm. If the surface layer 2 sis too thin, the effect based on the formation of the surface layer 2 sis insufficiently realized. On the other hand, if the surface layer 2 sis too thick, the medium is easily warped.

The surface layer 2 s may be formed by laminating an inorganic thin filmon a resin layer made of a radiation curable resin.

The thickness of the whole of the light-transmitting layer 2 isdetermined by requests of a recording/reproducing wavelength and arecording/reproducing optical system applied to the medium. It istherefore advisable to determine the thickness of the inner layer 2 i insuch a manner that the total thickness of the surface layer 2 s and theinner layer 2 i can satisfy the above requests.

The material which constitutes the surface layer 2 s may contain anon-crosslinking non-reactive lubricant, a water repellent, an oilrepellent, an antistatic agent, a leveling agent, a plasticizer or thelike. However, it is required that the added amount thereof isappropriately adjusted to fall the change rate of the contact anglebefore and after the above-mentioned sliding test based on theartificial fingerprint liquid component within the range of less than±10%. The appropriate added amount, which intensely depends on the kindsof the additives and the surface layer 2 s material, conditions forforming the surface layer 2 s, and others, cannot be determined withoutreservation. In general, however, the ratio of the various additives inthe hardened film is preferably 3% or less by weight, more preferably 1%or less by weight.

Preferably, the method for giving water repellency, oil repellency andlubricity to the laser beam incident side surface of the medium is, forexample, a method of forming the surface layer 2 s and subsequentlygiving water repellency, oil repellency and lubricity to the surface ofthe surface layer 2 s. In order to give water repellency, oil repellencyand lubricity to the surface of the surface layer 2 s, it is preferableto cause fluorine atoms to be present on the above surface.

Specifically, a silane coupling agent represented by the followingformula (I):R₁—Si(X)(Y)(Z)  (I)wherein R₁ is a substituent having water repellency, oil repellency andlubricity, X, Y and Z are each a monovalent group, and at least one ofX, Y and Z is a substituent capable of forming a chemical bond bypolycondensation with the hydroxyl group present on the surface of theunderlying (surface layer 2 s) on which the layer of the silane couplingagent is to be formed.

The substituent represented by R₁, which has water repellency, oilrepellency and lubricity, is a group which causes a compound whereinthis group is introduced to exhibit water repellency, oil repellency andlubricity. The water repellency and oil repellency of a material can berepresented into one way by the critical surface tension (γ_(c)/mNm¹),which is a criterion of the surface free energy of the material.

The water repellent, oil repellent and lubricant group represented by R₁is preferably a group having a fluorinated hydrocarbon group, andexamples thereof include fluorinated alkyl groups, and fluorinated alkylgroups containing a fluorinated alkyleneoxy group. The total carbonnumber thereof can be selected from the range of 1 to 5000. Thefluorinated hydrocarbon group may be in a normal chain form or abranched chain form, and is preferably in a normal chain form.

Specific examples of such a fluorinated hydrocarbon group may include afluorinated polyolefin segment represented by the following formula (II)or (III) and a fluorinated polyether segment represented by thefollowing formula (IV) or (V):CF₃(CF₂)_(x)CH₂CH₂—  (II)(CF₃)₂CF(CF₂)xCH₂CH₂—  (III)CF₃[OCF(CF₃)CF₂]x(OCF₂)y-  (IV)CF₃(OC₂F₄)x(OCF₂)y-  (V)

In the formulae (II) to (V), x and y are positive integers, and theseare preferably within the range of 0 to 200.

These have excellent water repellency, oil repellency and lubricity. Inparticular, about the carbon chain thereof, a chain in a long normalchain form, which has no branched structure, exhibits better waterrepellency, oil repellency and lubricity. The reactive groups in thesilane coupling agent, that is, X, Y and Z in Si(X) (Y) (Z) in theformula (I) are preferably substituents which are each capable offorming a chemical bond by polycondensation with a hydroxyl group, inparticular, substituents which are each capable of forming Si—O—Si bypolycondensation with the hydroxyl group which a silanol group has. Assuch a substituent, the following can be preferably selected: halogen,—OH (hydroxyl), —OR₂ (alkoxy), —OC(O)CH₃ (acetoxy), —NH₂ (amino), —N═C═O(isocyanic acid), or the like. R₂ is an alkyl group. Preferable examplesof the halogen include Cl and Br. The total carbon number of alkyl groupR₂ in —OR₂ is from 1 to 5, and the group may be in a normal chain formor in a branched chain form. The group may have a substituent which doesnot inhibit any chemically adsorbing reaction. For this reason, forexample, halogen is not preferable. Specific examples of —OR₂ includemethoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, and t-butoxy.

X, Y and Z may be the same or different from each other. When they aredifferent, they may be, for example, halogens different from each otheror alkoxy groups different from each other, or a mixture of two or threekinds of halogen, hydroxy, alkoxy, acetoxy, amino and isocyanic acid. Itis unnecessary that all of X, Y and Z are reactive substituents. It issufficient that at least one thereof is, for example, a hydrolyzablegroup of the above-mentioned halogen, alkoxy, hydroxy, acetoxy, amino orisocyanic acid. In order to form a strong siloxane bond network, all ofX, Y and Z are preferably the above-mentioned reactive groups. In thecase that X, Y or Z is not the above-mentioned reactive group, examplesof the monovalent group as X, Y or Z include a hydrogen atom and alkylgroups having 1 to 5 carbon atoms.

Such a silane coupling agent is, for example, a commercially availableproduct under a trade name of DSX (manufactured by Daikin Industries,Ltd.).

The method for forming the layer of the silane coupling agent is notparticularly limited, and an ordinary method can be used, example ofwhich include spin coating, dip coating, and spray coating. At the timeof the coating, the silane coupling agent may be appropriately dilutedwith a solvent.

The silane coupling agent layer has a thickness equivalent to that of amono molecular film or a super thin film close to it. The thickness isabout 1 to 20 nm.

In order to cause the silane coupling agent and the surface layer 2 s toconduct chemical absorbing reaction satisfactorily, it is preferable tomake the surface of the surface layer 2 s hydrophilic in advance by sucha method as plasma radiation, corona discharge treatment or electronbeam radiation.

As the method for giving water repellency, oil repellency and lubricityto the optical information medium surface, there can also be preferablyused a method of fluorinating the surface of the surface layer 2 s byplasma treatment using a fluorine compound. The present method is amethod of subjecting the surface layer 2 s to surface treatment withplasma of a fluorine compound, a typical example of which istetrafluoroethane. In this treatment, the following advance(s): thefluorination of the surface layer 2 s per se, and/or the precipitationof a polymer of the fluorine compound on the surface layer 2 s surface.As the fluorine compound used, preferable is an organic fluorinecompound, a typical example of which is tetrafluoromethane (CF₄) ortetrafluoroethylene (C₂F₄), or an inorganic fluorine compound such asSF₆ or NF₃.

Besides, the following method may also be used: a method of forming alubricant layer made of a fluorine-containing polymer such asperfluoropolyether, a silicone polymer such as polydimethylsiloxane, orthe silane coupling agent on the surface of the surface layer 2 s bycoating, and subsequently conducting plasma discharge treatment, therebyforming strong chemical bonds in the interface between the surface layer2 s and the lubricant layer. As a plasma supplying source in the plasmadischarge treatment, there may be used a compound containing no fluorineatom, such as methane (CH₄), ammonia (NH₃), or diborane (B₂H₆) besidesthe above-mentioned various fluorine-containing compounds. Aboutlubricant layer constituting materials such as fluorine-containingpolymer and silicone polymer, it is not particularly limited whether ornot the materials have a reactive terminal group such as a carboxylgroup, an isocyanate group or an acryloyl group. A commerciallyavailable product of the fluorine-containing polymer is, for example, aFomblin Z60 manufactured by Ausimont K.K., and a commercially availableproduct of the silicon polymer is, for example, a KF-96 manufactured byShin-Etsu Chemical Co., Ltd.

In the case that the surface layer 2 s per se has water repellency, oilrepellency and lubricity, the above-mentioned surface treatment may notbe conducted. The case that the surface layer 2 s per se has waterrepellency, oil repellency and lubricity is, for example a case whereinthe surface layer 2 s is formed using materials as described below.

The surface layer 2 s which per se has water repellency, oil repellencyand lubricity may be a layer containing a compound having a polymer mainchain wherein the polymer main chain and/or a side chain exhibits waterrepellency, oil repellency and lubricity. Specific examples thereof arepreferably substances wherein a water repellent, oil repellent andlubricant group such as a perfluoroalkyl group is introduced into a sidechain of a polymer compound such as polymethyl methacrylate,polycarbonate, or amorphous polyolefin. It is also allowable to use aradiation curable resin such as an ultraviolet curable resin to form thesurface layer 2 s; disperse fine particles made of an inorganic materialor a resin in this resin; and further modify the surfaces of the fineparticles with a substance containing a water repellent, oil repellentand lubricant substituent such as a fluorinated hydrocarbon. By applyingsuch a radiation curable resin and curing the resin, the surface layer 2s having water repellency, oil repellency and lubricity can be formed.In this case, a preferable particle size of the fine particles and apreferable ratio of the fine particles in the surface layer 2 s are thesame as in the above-mentioned case, wherein inorganic fine particlessuch as colloidal silica are dispersed in the surface layer 2 s.

The surface layer 2 s may be made up to a film made of DLC (Diamond LikeCarbon). The DLC film can be formed by a method known in the prior art,such as sputtering or CVD. Since the DLC thin film is high in surfacehardness and excellent in abrasion resistance and simultaneously thefilm can make the fraction coefficient of the surface low, the varioussurface treatments for giving lubricity may not be conducted.

The above-mentioned embodiment of the light-transmitting layer makes itpossible to produce an optical information medium which is excellent infingerprint removing property and has practically sufficient abrasionresistance.

EXAMPLES

The present invention will be more specifically described by way of thefollowing examples. However, the present invention is not limited tothese examples.

Example 1 Artificial Fingerprint Liquid

In Example 1, an optical recording disk is selected as an object to beevaluated, and the usefulness of the artificial fingerprint liquid ofthe present invention is described.

Optical recording disk samples No. 0 and No. 1 of two kinds, which havedifferent laser beam incident side surfaces, were separately produced asfollows. The layer structure of the optical recording disks isillustrated in FIG. 3.

In FIG. 3, an optical disk 1 has a reflective layer 3, a seconddielectric layer 52, a recording layer 4, a first dielectric layer 51,in this order, on one surface side of a supporting substrate 20 on whichfine concave-convex such as information pits or pregrooves are made; hasa resin layer 7 on the first dielectric layer 51; and has alight-transmitting layer 2 on the resin layer 7. The optical disk 1 isused in the state that recording or reproducing laser light is madeincident thereon through the light-transmitting layer 2. In disk sampleNo. 0, the light-transmitting layer 2 is made of a single layer of onlyan inner layer 2 i. In disk sample No. 1, the light-transmitting layer 2is made mainly of two layers of an inner layer 2 i and a surface layer 2s.

[Production of Disk Sample No. 0]

The reflective layer 3 made of Al₉₈Pd₁Cu₁ (atomic ratio) and having athickness of 100 nm was formed by sputtering on the surface of thedisk-form supporting substrate 20 (made of polycarbonate, diameter: 120mm, thickness: 1.2 mm) in which grooves were made. The depth of theabove grooves, which is represented by light-path length at wavelengthλ=405 nm, was set into λ/6. The recording track pitch in thegroove-recording scheme was set into 0.3 μm.

Next, an Al₂O₃ target was used to form the second dielectric layer 52having a thickness of 20 nm on the surface of the reflective layer 3 bysputtering. An alloy target made of a phase-change material was used toform the recording layer 4 having a thickness of 12 nm on the surface ofthe second dielectric layer 52 by sputtering. The composition of therecording layer 4 (atomic ratio) was set into Sb₇₄Te₁₈(Ge₇In₁). A ZnS(80% by mole)-SiO₂ (20% by mole) target was used to form the firstdielectric layer 51 having a thickness of 130 nm on the surface of therecording layer 4 by sputtering.

Next, a radical polymerizable ultraviolet curable resin solution(4X108E, manufactured by Mitsubishi Rayon Co., Ltd., solvent: butylacetate) was applied onto the surface of the first dielectric layer 51by spin coating, so as to form the resin layer 7 in such a manner thatthe thickness thereof would be 2.0 μm after being cured.

Next, in vacuum (0.1 atmospheric pressure or less), a polycarbonatesheet having a thickness of 100 μm was put on the resin layer 7. As thepolycarbonate sheet, a Pure Ace, manufactured by Teijin Ltd., producedby a flow casting method, was used. Next, the circumstance was returnedto the pressure of the atmosphere, and ultraviolet rays were radiatedthereon to cure the resin layer 7, thereby bonding the layer to thepolycarbonate sheet. This was made into the light-transmitting layer 2made of only the inner layer 2 i. In this way, disk sample No. 0 wasproduced.

[Production of Disk Sample No. 1]

The same procedure as in the production of disk sample No. 0 wasperformed till the formation of the inner layer 2 i made of thepolycarbonate sheet.

An ultraviolet curable resin SD-318 (manufactured by Nippon Kayaku Co.,Ltd.) was applied onto the surface of the inner layer 2 i by spincoating. Ultraviolet rays were radiated thereon to cure the resin,thereby forming a hard coat layer. The film thickness of the cured hardcoat layer was 2.0 μm. Next, a SiO₂ target was used to form a SiO₂ layerhaving a thickness of 100 nm on the surface of the hard coat layer bysputtering. Before the formation of the SiO₂ layer, the hard coat layersurface was subjected to activating treatment with plasma etching. Inthis sample, the surface layer 2 s was composed of the hard coat layerand the SiO₂ layer.

Furthermore, a silane coupling agent was chemically adsorbed on thesurface of the SiO₂ layer as follows. A DSX (manufactured by DaikinIndustries, Ltd.) having a water repellent and oil repellent group madeof a fluorine-containing hydrocarbon was used as the silane couplingagent. A 0.1% (percentage by mass) solution thereof in perfluorohexanewas applied thereto by spin coating, and the resultant was heated at 60°C. in the air for 10 hours so as to cause the silane coupling agent tobe chemically adsorbed on the above SiO₂ surface. In this way, producedwas the light-transmitting layer 2 composed of the inner layer 2 i andthe surface layer 2 s, wherein the silane coupling agent was chemicallyadsorbed on the surface of the surface layer 2 s. In this way, disksample No. 1 was produced.

Disk sample No. 1 had a better property for removing adheringfingerprints than disk sample No. 0 since the surface layer 2 s havingwater repellency and oil repellency was formed on disk sample No. 1.

[Evaluation of Surfaces of the Disk Samples, using ArtificialFingerprint Liquids]

(Preparation of Artificial Fingerprint Liquids)

To 10 g of methoxypropanol as a diluent was added 1.0 g of triolein, andthereto was further added 400 mg of Kanto loam of class 11 testingpowder 1 prescribed in JIS Z8901. The mixture was stirred to yieldartificial fingerprint liquid “a” (the present invention).

To 5 g of methoxypropanol as a diluent was added 200 mg of triolein, andthereto was further added 200 mg of keratin (originating from humanepithelia, manufactured by Wako Pure Chemicals, Industries). The mixturewas stirred, vigorously vibrated, and then allowed to stand still for 10seconds. Next, the supernatant portion thereof in which keratin havinglarge particle sizes was not present was quietly collected to yieldartificial fingerprint liquid “b” (the present invention).

To 10 g of methoxypropanol as a diluent was added 1.0 g of triolein toyield artificial fingerprint liquid “c” (comparison).

(Formation of Original Plates for Pseudo Fingerprint Pattern Transfer)

About each of artificial fingerprint liquids “a”, “b” and “c”, anoriginal plate for pseudo fingerprint pattern transfer was formed asfollows. While artificial fingerprint liquid “a” was sufficientlystirred with a magnetic stirrer, about 1 mL thereof was collected. Thecollected liquid was applied onto a polycarbonate substrate (diameter:120 mm, thickness: 1.2 mm) by spin coating. This substrate was heated at60° C. for 3 minutes to remove methoxypropanol, which was the diluentwhich had become unnecessary, completely. In this way, original plate“a” for pseudo fingerprint pattern transfer was obtained. Aboutartificial fingerprint liquids “b” and “c”, original plates “b” and “c”for pseudo fingerprint pattern transfer were obtained, respectively, inthe same way.

(Transfer and Wipe of the Pseudo Fingerprint Patterns)

As a pseudo fingerprint transferring stamp, there was used a productwherein a smaller end face (diameter: 12 mm) of a No. 1 silicone rubberplug was uniformly polished with a #240 abrasive paper (having the sameperformance as an AA240 abrasive paper described in the above JIS). Thepolished end face of the pseudo fingerprint transferring stamp waspressed against original plate “a” at a load of 29 N for 10 seconds totransfer components of the artificial fingerprint liquid to the end faceof the transferring stamp. Next, the end face of the transferring stamp,onto which the artificial fingerprint liquid components adhered, waspressed against an area of the light-transmitting layer 2 surface ofdisk sample No. 0, the area being located about 40 mm apart in theradius direction from the center thereof, at a load of 29 N for 10seconds so as to transfer the artificial fingerprint liquid “a”component. About disk sample No. 1, the artificial fingerprint liquid“a” component was transferred thereto in the same way.

In the same way, the original plates “b” and “c” were separately used totransfer artificial fingerprint liquid components onto respective disksamples No. 0 and No. 1.

Next, the artificial fingerprint liquid components adhering onto therespective disk samples were wiped off in the following steps. A productobtained by putting 8 pieces of commercially available tissue paper(manufactured by Crecia Corp.) on each other was sandwiched between alarger end face (diameter: 16 mm) of the No. 1 rubber plug and thelight-transmitting layer 2 surface onto which the artificial fingerprintliquid component adhered, and the resultant was pressed at a strength of4.9 N. In this state, the rubber plug was slowly shifted from the centerof the disk sample to the outer circumference thereof to wipe off theadhering artificial fingerprint liquid component.

About each of the disk samples, the jitter of recorded signals wasmeasured at the following separate times: a time before the artificialfingerprint liquid component adhered (initial), a time immediately afterthe artificial fingerprint liquid component adhered (before the wipe),and times after performing the wiping-off operation 2 times, 5 times, 10times and 15 times. The results are shown in Table 1.

Respective parameters of the optical system of an optical informationmedium evaluating system used to record and reproduce signals, andrecording/reproducing conditions are as follows.

-   Laser wavelength: 405 nm-   Numerical aperture NA of objective lens: 0.85-   Linear velocity: 6.5 m/s-   Recording signal: 1-7 modulating signals (shortest signal length:    2T)

Recording areas: Lands and grooves (Table 1 shows only measurementresults of the groove portions) TABLE 1 Jitter (unit: %) Immediatelyafter the After After After After After Disk adhesion of wiping thewiping the wiping the wiping the wiping the sample Initial the finger-liquid liquid liquid liquid liquid No. stage print liquid one time 2times 5 times 10 times 15 times Artificial fingerprint 0 7.2 22.0 14.110.3 8.8 8.7 9.2 liquid “a” 1 7.1 22.1 9.4 7.8 7.4 7.2 7.2 (the presentinvention) Artificial fingerprint 0 7.1 24.0 13.7 8.8 8.5 8.2 8.9 liquid“b” 1 7.2 23.5 9.1 7.5 7.2 7.1 7.1 (the present invention) Artificialfingerprint 0 7.1 11.1 9.7 7.5 7.9 8.5 9.1 liquid “c” 1 7.2 15.8 9.8 7.97.2 7.2 7.2 (comparison)

Table 1 demonstrates that when artificial fingerprint liquid “a” or “b”of the present invention is used, it can be quantitatively determinedusing the jitter value that disk sample No. 1 is better in the propertyfor removing the adhering artificial fingerprint liquid component thandisk sample No. 0 since the surface layer 2 s having water repellent andoil repellent performance is formed in disk sample No. 1. It can bequantitatively determined using the jitter value that about disk sampleNo. 1, as the number of the wiping operations is more, the adheringartificial fingerprint liquid component is removed in a more amount sothat the initial performance of the optical disk can be restored. Thereason why about disk sample No. 0 the jitter value deterioratedslightly after the number of the wiping operations became 15 can beconsidered as follows: since the hardness of the light-transmittinglayer 2 of sample No. 0 was low, scratches were generated in the surfaceby the wiping operations.

On the other hand, in the case that artificial fingerprint liquid “c”was used, the artificial fingerprint liquid component was not fixed onthe light-transmitting layer 2 surface and about both of disk samplesNo. 0 and No. 1 the jitter values after wiping this fingerprint liquidone time were substantially equal. As described above, water repellentand oil repellent performances between disk samples cannot bedistinguished. Thus, artificial fingerprint liquid “c” is unsuitable asan artificial fingerprint liquid used to evaluate surface performances.

In this Example 1, the optical recording disks were used as the objectsto be evaluated, and the usefulness of the artificial fingerprint liquidof the present invention was shown. The artificial fingerprint liquid ofthe present invention can be used to evaluate, quantitatively and with agood reproducibility, the anti-staining property, and the fingerprintadhering property or the fingerprint removing property of not only theoptical recording disks but also various other surfaces. Thus, Example 1is a mere example in all ways, and the present invention should not beinterpreted as being limited thereto. Furthermore, all modificationsbelonging to a scope equivalent to that of the claims are within thescope of the present invention.

Example 2 Production of Optical Information Media having ImprovedFingerprint Removing Property

Each of optical recording disk samples having the layer structureillustrated in FIG. 3 was produced in the manner described below. Insample No. 0, however, its light-transmitting layer 2 was made to have asingle-layered structure.

-   Sample No. 0: the same as disk sample No. 0 produced in Example 1-   Sample No. 1: the same as disk sample No. 1 produced in Example 1    [Production of Sample No. 2]

The same procedure as in the production of disk sample No. 0 wasperformed till the formation of the inner layer 2 i made of thepolycarbonate sheet.

A Desolight Z7503 (manufactured by JSR Co., Ltd.) was applied, as anultraviolet curable resin in which colloidal silica was dispersed, ontothe surface of the inner layer 2 i by spin coating, and dried at 60° C.for 3 minutes to remove the diluting solvent. Thereafter, ultravioletrays were radiated thereon to cure the resin, thereby forming thesurface layer 2 s. The film thickness after being cured was 3.0 μm.

Next, fluorine plasma treatment was applied to the surface of thesurface layer 2 s. As the fluorinated compound, tetrafluoromethane (CF₄)was used. The inside of a chamber of the plasma treatment device wasdegassed and then CF₄ gas was introduced into the chamber to adjust thepressure into 0.5 Pa. Next, an RF electric field was applied thereto soas to conduct the plasma treatment at a power of 100 W. The time for thetreatment was set into 3 minutes. After the end of the plasma treatment,the inside of the chamber was returned to the normal pressure, and thedisk was taken out.

[Production of Sample No. 3]

The same procedure as in the production of disk sample No. 0 wasperformed till the formation of the inner layer 2 i made of thepolycarbonate sheet.

An ultraviolet curable resin (HOD 3200 manufactured by Nippon KayakuCo., Ltd.) was applied, as a primer, onto the inner layer 2 i, and thencured by radiation of ultraviolet rays. The film thickness of the resinafter being cured was 0.5 μm.

Next, a thermosetting silicone coating agent (Fllesera D, manufacturedby Matsushita Electric Industrial Co., Ltd.) was applied onto the primerlayer by spin coating, and heated at 80° C. for 2 hours so as to bedried and set. In this way, the surface layer 2 s was formed. Thethickness of the surface layer 2 s was 1.0 μm.

The above-mentioned silicone coating agent has a structure wherein alubricant, water repellent and oil repellent group is introduced intothe silicon atom of an organic silicon compound which is a monomercomponent, and the coating after being set has a structure wherein thelubricant, water repellent and oil repellent group is fixed through achemical bond to the silicon atom of a polysiloxane bond.

[Production of Sample No. 4]

The same procedure as in the production of disk sample No. 0 wasperformed till the formation of the inner layer 2 i made of thepolycarbonate sheet.

A DLC thin film having a thickness of 360 nm was formed as the surfacelayer 2 s on the inner layer 2 i by plasma CVD. As the process gas,ethylene (C₂H₄) was used. The inside of a chamber of the plasmatreatment device was degassed and then ethylene gas was introduced intothe chamber to adjust the pressure into 0.5 Pa. Next, an RF electricfield was applied thereto so as to form the film by CVD at a power of100 W. The time for the treatment was set into 3 minutes. After the endof the plasma treatment, the inside of the chamber was returned to thenormal pressure, and the disk was taken out.

[Production of Sample No. 5]

An optical recording disk sample was produced in the same way forproducing sample No. 1 except that no silane coupling agent layer wasformed on the surface of the SiO₂ layer.

[Production of Sample No. 6]

The same procedure as in the production of disk sample No. 0 wasperformed till the formation of the inner layer 2 i made of thepolycarbonate sheet.

An ultraviolet curable resin (SD 318 manufactured by Nippon Kayaku Co.,Ltd.) was applied onto the inner layer 2 i by spin coating, and thencured by radiation of ultraviolet rays, so as to form the surface layer2 s having a thickness of 2.0 μm.

Next, a solution wherein silicone oil (KF96, manufactured by Shin-EtsuChemical Co., Ltd., viscosity: 10000 cP) was diluted with butyl acetatewas applied onto the surface of the surface layer 2 s by spin coating,so as to form a layer having water repellency, oil repellency andlubricity. In this way, an optical recording disk sample was produced.The amount of the applied silicone oil was 32 mg/m², and the thicknessof the formed layer was 33 nm.

[Production of Sample No. 7]

The same procedure as in the production of disk sample No. 0 wasperformed till the formation of the inner layer 2 i made of thepolycarbonate sheet.

An ultraviolet curable resin (SD 318 manufactured by Nippon Kayaku Co.,Ltd.) was applied onto the inner layer 2 i by spin coating, and thencured by radiation of ultraviolet rays, so as to form the surface layer2 s having a thickness of 2.0 μm.

Next, a solution wherein a perfluoropolyether derivative (Fonbrin ZDOL,manufactured by Ausimont K. K.) was diluted with a fluorine type solvent(H-GALDEN ZV100, manufactured by Ausimont K.K.) was applied onto thesurface of the hard coat layer by spin coating, so as to form a layerhaving water repellency, oil repellency and lubricity. In this way, anoptical recording disk sample was produced. The amount of the appliedperfluoropolyether derivative was 35 mg/m², and the thickness of theformed layer was 19 nm.

[Production of Sample No. 8]

An optical recording disk sample was produced in the same way forproducing sample No. 2 except that no fluorine plasma treatment wasconducted.

[Production of Sample No. 9]

Instead of the silane coupling agent DSX used in sample No. 1,trifluoromethyltrimethoxysilane (CF₃Si(OCH₃) 3) was used. A coatingsolution was prepared by dissolving trifluoromethyltrimethoxysilane intom-xylenehexafluoride so as to have a concentration of 0.1% by mass. Inthe same way for producing sample No. 1 except this, an opticalrecording disk sample was produced.

[Evaluation]

About each of the above-mentioned optical disk samples, the contactangle of water to its light-transmitting layer surface and the changerate (deterioration degree) thereof were measured according to thefollowing procedure.

First, a silicone rubber plug the end face of which had a diameter of 16mm was covered with a dried cloth (Bemcot Lint Free CT-8, manufacturedby Asahi Chemical Co., Ltd.), and the portion of the cloth with whichthe vicinity of the silicone rubber plug end face was covered wasimpregnated with 2.0 mL of an artificial fingerprint liquid. Thisartificial fingerprint liquid was a liquid obtained by adding 4.0 g ofKanto loam of class 11 testing powder 1 prescribed in JIS Z8901 to 10 gof triolein and stirring the resultant sufficiently. The Kanto loamcontains, as main components thereof, SiO₂, Fe₂O₃, Al₂O₃ and others, andthe median diameter thereof is from 1.6 to 2.3 μm. Next, the end face ofthe silicone rubber plug was pressed perpendicularly to the surface ofthe light-transmitting layer surface of each of the samples at a load of4.9 N/cm² with the cloth impregnated with the artificial fingerprintliquid component being sandwiched therebetween, and slid 50 times in areciprocating motion along the radius direction of the sample.

Next, the silicone rubber plug and cloth were newly prepared, and thecloth was impregnated with 2.0 mL of ethanol in the same way asdescribed above. Thereafter, the end face of the silicone rubber waspressed to the portion previously scrubbed with the cloth containingtriolein at a load of 2.5 N/cm² with the cloth impregnated with ethanolbeing sandwiched therebetween. The end face was slid 20 times in theradius direction of the sample.

Next, the cloth was exchanged with a new cloth. The cloth wasimpregnated with ethanol in the same way as described above, and thecloth was again slid 20 times on the same portion. Ethanol wascompletely dried and then static electricity was removed by an ionizer.Thereafter, the contact angle was measured. The measurement of thecontact angle was performed under the environment having a temperatureof 20° C. and a relative humidity of 60%, using a contact angle meterCA-D manufactured by Kyowa Interface Science Co., Ltd. The results areshown in Table 2. Table 2 also shows the change rate of the contactangle. This change rate is the percentage of a value calculated from thefollowing equation, using the initial contact angle and the contactangle after the artificial fingerprint liquid was adhered and wiped off(the contact angle after the sliding in Table 2):(value after the sliding−initial value)/initial value

The kinetic friction coefficient of the light-transmitting layer surfacewas measured according to the following procedure. A nylon chip the tipof which had a curvature radius of 5 mm was formed and this was broughtinto contact with the light-transmitting layer surface of each of thesamples at a constant load, and the sample was, as it was, rotated at aconstant speed. From the load and the torque at this time, the kineticfriction coefficient was calculated. For the measurement, a remodeledoptical disk driving device was used. The nylon chip was fitted to theoptical head section of the driving device. The device was made to makeit possible to measure the torque applied to the chip When the nylonchip was slid on the sample surface, that is, the frictional force Fdwith a torque meter. In this measurement, the load (normal-force Fp)when the nylon chip was brought into contact with the sample surface wasset into 20 mN, and the linear velocity when the sample was rotated wasset into 1.4 m/s. The kinetic friction coefficient μ can be obtainedfrom Fd/Fp.

The kinetic friction coefficient was measured at the initial stage andafter the artificial fingerprint liquid was adhered and wiped off (afterthe sliding) in the same way as in the measurement of the contact angle.The initial kinetic friction coefficient, the kinetic frictioncoefficient after the sliding, and a difference between the two (changequantity) are together shown in Table 2. TABLE 2 Contact angle Kineticfriction coefficient Initial After the Change Sample Pencil ΔHazeInitial After the Change stage sliding rate No. hardness (%) stagesliding quantity (deg) (deg) (%) 0 B 38.2* —¹⁾ —¹⁾ — 83.2 81.5 −2.0 1 HB3.2 0.23 0.24 0.01 113.5 112.0 −1.3 2 HB 2.0 0.25 0.38 0.01 106.4 102.8−3.4 3 HB 5.1 0.22 0.24 0.02 104.6 102.1 −2.4 4 HB 6.7 0.34 0.35 0.0179.8 79.5 −0.4 5 HB 3.3 0.55* 0.53 −0.02 18.5* 18.0 −2.7 6 HB 8.5 0.200.56 0.36* 87.2 70.1 −19.6* 7 HB 8.9 0.35 0.60 0.35* 100.2 74.2 −25.9* 8HB 2.1 0.81* 0.78 −0.03 72.5* 72.0 −0.7 9 HB 3.0 0.48* 0.49 0.01 113.8112.5 −1.1¹⁾Unable to be measured since the light-transmitting layer surface wasinjured immediately after the chip was slid*Outside the limited range

As is evident from Table 2, in samples No. 1 and No. 2, the substituenthaving water repellency, oil repellency and lubricity was fixed to thesurface layer 2 s (or the surface layer 2 s per se had water repellency,oil repellency and lubricity); therefore, the contact angle hardlydeteriorated even if they were scrubbed with the cloth impregnated withtriolein, and further the kinetic friction coefficient thereof hardlychanged. On the other hand, in samples No. 6 and No. 7, the waterrepellency, oil repellency and lubricity were kept by the lubricantlayer formed on the surface and having fluidity; therefore, the contactangle were easily lowered by the sliding of the cloth impregnated withtriolein, and further the kinetic friction coefficient thereofincreased. It is presumed from these results that when a fingerprintadheres, the fingerprint components are mixed with the lubricant so thatit becomes difficult to wipe off the fingerprint. In sample No. 5, thelight-transmitting layer surface was made of the glass components. Thus,the initial contact angle was very small.

Example 3 Method for Evaluating Fingerprint Removing Property of OpticalInformation Media

About samples No. 0 to No. 9 produced in Example 2, the fingerprintremoving property of the light-transmitting layer surface thereof wasevaluated by a method described below.

There were used the same artificial fingerprint liquid “a” (the presentinvention), the artificial fingerprint liquid “b” (the presentinvention) and the artificial fingerprint liquid “c” (comparison)prepared in Example 1.

About the artificial fingerprint liquids “a”, “b” and “c”, originalplates “a”, “b” and “c” for pseudo fingerprint pattern transfer wereobtained, respectively, by the same operation as in Example 1. Each ofthe original plates “a”, “b” and “c” was used to transfer artificialfingerprint liquid components onto each of disk samples No. 0 to No. 9by the same operation as in Example 1.

Next, the artificial fingerprint liquid components adhering to thesurface of each of the disk sample surfaces were wiped off by the sameoperation as in Example 1.

About each of the disk samples, the jitter of recorded signals wasmeasured at the following separate times: a time before the artificialfingerprint liquid components adhered (initial), a time immediatelyafter the artificial fingerprint liquid components adhered (before thewipe), and times after performing the wiping-off operation 2 times, 5times, 10 times and 15 times. The results are shown in Table 3. Resultswhen the pseudo fingerprint component “a” was used are also shown inFIG. 4.

Respective parameters of the optical system of an optical informationmedium evaluating system used to record and reproduce signals, andrecording/reproducing conditions are as follows.

-   Laser wavelength: 405 nm-   Numerical aperture NA of objective lens: 0.85-   Linear velocity: 6.5 m/s-   Recording signal: 1-7 modulating signals (shortest signal length:    2T)-   Recording areas: Lands and grooves (Table 3 shows only measurement    results of the groove portions)

A sensuous evaluation (sensory test) was also made on the fingerprintremoving easiness. First, each of the artificial fingerprint liquidcomponents was adhered to the surface of each of the samples under theabove-mentioned conditions. Next, about these samples, 5 monitorsselected at will made a wiping-off test, and evaluated the wiping-offeasiness into 3 ranks. The results are shown in Table 4. The standard ofthe evaluation shown in Table 4 is as follows:

-   -   A: A fingerprint is very easily wiped off.    -   B: A fingerprint is easily wiped off.    -   C: A fingerprint is not easily wiped off.

Commercially available tissue paper (manufactured by Crecia Corp.) wasused for the wiping-off, and the number of the wiping operations and thewiping load were not particularly specified. TABLE 3 Jitter (unit: %)Immediately after the After After After After After adhesion of wipingthe wiping the wiping the wiping the wiping the Sample Initial thefinger- liquid liquid liquid liquid liquid No. stage print liquid onetime 2 times 5 times 10 times 15 times Artificial 0 7.2 22.0 14.1 10.38.8 8.7 9.2 fingerprint 1 7.1 22.1 9.4 7.8 7.4 7.2 7.2 liquid “a” 2 7.221.0 9.6 8.2 7.5 7.1 7.2 3 7.2 22.7 10.1 8.5 7.8 7.5 7.3 4 7.1 22.9 13.89.8 8.8 7.6 7.3 5 7.0 19.5 15.2 12.3 9.8 8.2 7.6 6 7.2 23.0 16.0 12.211.7 9.7 9.3 7 7.2 22.0 16.7 13.2 10.5 9.5 9.0 8 7.2 22.1 14.5 10.5 9.27.6 7.3 9 7.2 21.2 9.6 8.8 7.6 7.1 7.1 Artificial 0 7.1 11.1 9.7 7.5 7.98.5 9.1 fingerprint 1 7.2 15.8 9.8 7.9 7.2 7.2 7.2 liquid “c” 2 7.2 15.310.0 8.2 7.5 7.2 7.2 (comparison) 3 7.1 14.3 10.2 8.1 7.3 7.2 7.1 4 7.112.0 9.5 8.3 7.2 7.3 7.1 5 7.1 10.2 9.5 7.5 7.1 7.1 7.1 6 7.2 16.1 11.08.2 7.4 7.2 7.2 7 7.2 15.7 12.3 8.3 7.5 7.1 7.2 8 7.2 11.8 11.3 7.9 7.87.2 7.2 9 7.2 16.2 9.4 7.5 7.1 7.2 7.1 Artificial 0 7.1 24.0 13.7 8.88.5 8.2 8.9 fingerprint 1 7.2 23.5 9.1 7.5 7.2 7.1 7.1 liquid “b”

TABLE 4 Sensuous evaluation/ Kinetic friction the number of personsSample No. coefficient A B C 0 Unable to be measured 0 1 4 1 0.23 5 0 02 0.25 5 0 0 3 0.22 5 0 0 4 0.34 3 2 0 5 0.55* 0 2 3 6 0.20 4 1 0 7 0.353 2 0 8 0.81* 0 0 5 9 0.48* 1 2 2A: A fingerprint is very easily wiped off.B: A fingerprint is easily wiped off.C: A fingerprint is not easily wiped off.*Outside the limited range

About samples No. 1 to No. 4, wherein the contact angle of thelight-transmitting layer 2 surface and the change rate thereof werewithin the given ranges in Table 2, evaluation was made using artificialfingerprint liquid component “a” as shown in Table 3 and FIG. 4. In thiscase, the jitter of recorded signals was restored to a levelsubstantially equal to that before the adhesion of the fingerprintimmediately after the wiping-off of the pseudo fingerprint 2 or 5 times.On the other hand, about the samples other than them, in particular,samples No. 6 and No. 7, which had high water repellency, oil repellencyand lubricity, the jitter thereof was not restored to the initial valueby the operation of wiping off the fingerprint 15 times. It is evidentfrom these facts that the fingerprint removing property does not dependon only the water repellency and the oil repellency, that is, only themagnitude of the surface energy. In other words, in the case that thewater repellency and the oil repellency are realized by fluid materialsin the lubricant layer formed on the surface, a layer resulting fromexudation of water repellent and oil repellent agents, which arepreviously added to the material of the light-transmitting layer, to thesurface, and other layers even if the water repellency and the oilrepellency are high, the fingerprint removing property deterioratesinversely.

On the other hand, in the case that evaluation was made using artificialfingerprint liquid component “c”, which was made of an homogeneoussystem containing no Kanto loam, the artificial fingerprint liquidcomponent was not fixed on the light-transmitting layer 2 surface andall of the samples had the same wiping-off property as is clear form theresults shown in Table 3. In other words, in this case, actualfingerprint adhering property and removing property cannot be reproducedor quantitatively analyzed. Evidently, it is unsuitable as a testingmethod for optical information media.

About sample No. 0, the initial contact angle was within the given rangein Table 2, and the contact angle after the sliding based on theartificial fingerprint liquid component hardly deteriorated. However,scratches were generated in the surface by the wiping-off operationsince the hardness of the light-transmitting layer surface was low.Therefore, when the artificial fingerprint liquid was wiped off morethan 10 times, the jitter deteriorated reversely.

As shown in Table 4, the fingerprint removing property sensuously judgedby the users was not necessarily consistent with the rank shown in Table3. For example, when samples No. 1 and No. 9 were compared with eachother, the two were excellent in water repellency and oil repellency andthe surface hardness of the light-transmitting layer was also high.However, it is judged in Table 4 that about sample No. 1 the fingerprintthereon was very easily wiped off whereas it is judged that about sampleNo. 9 the fingerprint was not necessarily easily wiped off. This isbecause the kinetic friction coefficient of the light-transmitting layer2 surface of sample No. 9 was high. It is therefore evident from theseresults that in order to make the fingerprint removing property whichusers sensuously judges very good, it is necessary not only to make thewater repellency, oil repellency and hardness high but also to decreasethe kinetic friction coefficient.

When pseudo fingerprint component “b”, which contained keratin insteadof the inorganic particle-form-material was used, substantially the sameresults as in the case of using pseudo fingerprint component “a” wereobtained. It is clear from these results that the present invention, inwhich the artificial fingerprint liquid component containing aninorganic particle-form substance is used, makes it possible to simulatethe influence of the adhesion of actual fingerprints quantitatively andwith a good reproducibility.

The above-mentioned Examples are mere examples in all points, and thepresent invention should not be restrictedly interpreted. Furthermore,all modifications belonging to a scope equivalent to that of the claimsare within the scope of the present invention.

INDUSTRIAL APPLICABILITY

According to the present invention, provided is a low-cost artificialfingerprint liquid for quantitatively and with a good reproducibilityevaluating an anti-staining property, and a fingerprint adheringproperty or a fingerprint removing property on the surface of an opticaldisk such as a reproduction-only optical disk, optical recording disk,magneto-optical recording disk, various displays such as a CRT, andvarious substances such as glass.

In the testing method of the present invention, influence whichrecording/reproducing signals receive when a fingerprint adheres to anoptical information medium can be measured quantitatively and with agood reproducibility. Furthermore, the optical information medium of thepresent invention can maintain good recording/reproducing property overa long period since the medium has a good property for wiping offorganic stains adhering to the surface thereof, such as a fingerprint.

1-17. (canceled)
 18. An optical information medium which comprises alight-transmitting layer and an information recording layer and is usedto make a recording/reproducing beam incident into the informationrecording layer through the light-transmitting layer, wherein when anartificial fingerprint liquid comprising a fine-particle-form substanceand a dispersion medium capable of dispersing the fine-particle-formsubstance is adhered onto the surface of the light-transmitting layerand subsequently an operation for removing the adhered artificialfingerprint liquid is performed, the kinetic friction coefficient of thelight-transmitting layer surface after the removing operation does notincrease by 0.1 or more from the kinetic friction coefficient before theadhesion of the artificial fingerprint liquid.
 19. The opticalinformation medium according to claim 18, wherein when a compound havinglubricity is present on the light-transmitting layer surface, the amountof the portion not fixed on the light-transmitting layer surface amongthe entire compound is 20 mg/m² or less.
 20. The optical informationmedium according to claim 18, wherein when a layer including a compoundwhich has lubricity and is not fixed on the light-transmitting layersurface is present on the light-transmitting layer surface, thethickness of the above layer is 10 nm or less.
 21. The opticalinformation medium according to claim 18, wherein the kinetic frictioncoefficient of the light-transmitting layer surface is 0.4 or lessbefore the adhesion of the artificial fingerprint liquid.
 22. Theoptical information medium according to claim 18, wherein a Si—O bond ispresent in at least one portion of the light-transmitting layer surface.23. The optical information medium according to claim 18, wherein atleast one portion of the light-transmitting layer surface includes afluorine atom.
 24. The optical information medium according to claim 18,wherein at least one portion of the light-transmitting layer surface ismade of a silane coupling agent which includes a group exhibiting waterrepellency or oil repellency and which is represented by the followingformula (I):R₁—Si(X)(Y)(Z)  (I) wherein R₁ is a substituent having water repellency,oil repellency and lubricity, X, Y and Z are each a monovalent group,and at least one of X, Y and Z is a substituent capable of forming achemical bond by polycondensation with a hydroxyl group.
 25. The opticalinformation medium according to claim 18, wherein the light-transmittinglayer surface is fluorinated by plasma treatment.
 26. The opticalinformation medium according to claim 18, wherein at least one portionof the light-transmitting layer is made of diamond-like carbon.
 27. Theoptical information medium according to claim 18, which is used in asystem wherein the smallest diameter of a recording/reproducing beam onthe light-transmitting layer surface is 500 μm or less.
 28. The opticalinformation medium according to claim 18, wherein the kinetic frictioncoefficient of the light-transmitting layer surface is 0.4 or lessbefore the adhesion of the artificial fingerprint liquid.
 29. An opticalinformation medium which comprises a light-transmitting layer and aninformation recording layer and is used to make a recording/reproducingbeam incident into the information recording layer through thelight-transmitting layer, wherein when an artificial fingerprint liquidcomprising a fine-particle-form substance and a dispersion mediumcapable of dispersing the fine-particle-form substance is adhered ontothe surface of the light-transmitting layer and subsequently anoperation for removing the adhered artificial fingerprint liquid isperformed, the contact angle of water to the light-transmitting layersurface after the removing operation does not decrease by 15% or morefrom the contact angle thereof before the adhesion of the artificialfingerprint liquid.
 30. The optical information medium according toclaim 29, wherein when a compound having water repellency is present onthe light-transmitting layer surface, the amount of the portion notfixed on the light-transmitting layer surface among the entire compoundis 20 mg/m² or less.
 31. The optical information medium according toclaim 29, wherein when a layer including a compound which has waterrepellency and is not fixed on the light-transmitting layer surface ispresent on the light-transmitting layer surface, the thickness of theabove layer is 10 nm or less.
 32. The optical information mediumaccording to claim 29, wherein before the adhesion of the artificialfingerprint liquid, the contact angle of water to the light-transmittinglayer surface is 75° or more at 20° C.
 33. The optical informationmedium according to claim 29, wherein before the adhesion of theartificial fingerprint liquid, the contact angle of water to thelight-transmitting layer surface is 90° or more at 20° C.
 34. Theoptical information medium according to claim 29, wherein a Si—O bond ispresent in at least one portion of the light-transmitting layer surface.35. The optical information medium according to claim 29, wherein atleast one portion of the light-transmitting layer surface includes afluorine atom.
 36. The optical information medium according to claim 29,wherein at least one portion of the light-transmitting layer surface ismade of a silane coupling agent which includes a group exhibiting waterrepellency or oil repellency and which is represented by the followingformula (I):R₁—Si(X)(Y)(Z)  (I) wherein R₁ is a substituent having water repellency,oil repellency and lubricity, X, Y and Z are each a monovalent group,and at least one of X, Y and Z is a substituent capable of forming achemical bond by polycondensation with a hydroxyl group.
 37. The opticalinformation medium according to claim 29, wherein the light-transmittinglayer surface is fluorinated by plasma treatment.
 38. The opticalinformation medium according to claim 29, wherein at least one portionof the light-transmitting layer is made of diamond-like carbon.
 39. Theoptical information medium according to claim 29, which is used in asystem wherein the smallest diameter of a recording/reproducing beam onthe light-transmitting layer surface is 500 μm or less.